Prevent SysUI from crashing during Ghost animation

This CL prevents a crash in SysUI when starting a launch animation that
ghosts a View that is not attached to a ViewGroup. We now skip the
animation when that happens.

Bug: 192194319
Test: atest ActivityLaunchAnimatorTest
Test: atest GhostedViewLaunchAnimatorControllerTest
Change-Id: I6f2616776a092307c84d8f64fbbb798eb1bebafb